Internally safety reinforced cup grinding wheel

ABSTRACT

A resinoid bonded abrasive cup type grinding wheel with internal layers of safety reinforcing material integrally molded within, bonded to and tieing the central hub and sidewall portions of the wheel together. The safety reinforcement extends continuously, in a smoothly curved shape without sharp bends, generally radially outward through the central hub portion, and then generally axially and radially outward through the sidewall portion to an outer peripheral edge. The wheel is molded by supporting at least one layer of flexible reinforcing material between two layers of a curable mixture of abrasive and bond on a thin flexible supporting disk partially supported above a mold cavity by a fixed outer narrow top surface of a lower mold plate and an aligned movable support surface of a movable central hub support member resiliently biased into the mold cavity and slideable in the lower mold plate. During molding, the central hub forming portion of the mix is continuously held and slightly compacted between the central hub support member and an upper mold plate engaged by a platen of a press which forces them into and to a fixed stop at the bottom of the cavity. As the surrounding loose mix and layers of reinforcement, which are free to bend relative to the fixed outer annular surface, move into the cavity the abrasive mix shifts sufficiently to allow the reinforcement to assume a smoothly curved shape prior to being compressed to final size and shape.

eat

States Corcoran et a1.

[451 Mar. 4, 1975 1 INTERNALLY SAFETY REINFORCED CUP GRKNDING WHEEL [75]Inventors: John J. Corcoran, Ashland; Paul W. Kalinow'ski, Boylston,both of .Mass.

[52] U.S. Cl 51/209 R' [51] Int. Cl 324d 7/04 [58] Field of Search51/209 R, 206, 206 NF, 51/378,170 T, 170 PT [56] References Cited UNlTEDSTATES PATENTS 7 2,540,112 2/1951 Goepfert 51/206 2,997,820 8/1961 Skoog1 1 51/209 R 3,041,797 7/1962 Moffly 51/378 3,121,981 2/1964 Hurst51/209 X 3,136,100 6/1964 Robertson 51/209 R 3,431,687 3/1969 Fischer51/206 NF Primary Examiner-Donald G. Kelly Attorney, Agent, orFirm-Walter Fred [57] ABSTRACT A resinoid bonded abrasive cup typegrinding wheel with internal layers of safety reinforcing materialintegrally molded within, bonded to and tieing the central hub andsidewall portions of the wheel together. The safety reinforcementextends continuously, in a smoothly curved shape without sharp bends,generally radially outward through the central hub portion, and thengenerally axially and radially outward through the sidewall portion toan outer peripheral edge.

The wheel is molded by supporting at least one layer of flexiblereinforcing material between two layers of a curable mixture of abrasiveand bond on a thin flexible supporting disk partially supported above amold cavity by a fixed outer narrow top surface of a lower mold plateand an aligned movable support surface of a movable central hub supportmember resiliently biased into the mold cavity and slideable in thelower mold plate. During molding, the central hub forming portion of themix is continuously held and slightlycompacted between the central hubsupport member and an upper mold plate engaged by a platen of a presswhich forces them into and to a fixed stop at the bottom of the cavity.As the surrounding loose mix and layers of reinforcement, which are freeto bend relative to the fixed outer annular surface, move into thecavity the abrasive mix shifts sufficiently to allow the reinforcementto assume a smoothly curved shape prior to being compressed to finalsize and shape.

8 Claims, 3 Drawing Figures INTERNALLY SAFETY REINFORCED CUP GRINDINGWHEEL BACKGROUND OF THE INVENTION 1. Field of Invention The inventionrelates to cup shaped grinding wheels and particularly to an internallysafety reinforced resinoid bonded abrasive cup type grinding wheel,apparatus and method of making it.

2. Description of the Prior Art Although cup shaped grinding wheels areused with different types of grinding apparatus and for variouspurposes, the resinoid cup shaped wheel is normally attached to handoperated high speed portable snagging grinders for heavy duty roughgrinding off unwanted portions of castings, forgings, weldments and thelike. Since various abrasive surfaces of the wheel may be used to grindwith, it is obvious that those portions must be left unprotected andsubjected to possible fracture resulting from accidental impact withanother object. Thus when a fractured wheel is rotated at relativelyhigh speed, one or more fragments of the wheel are likely to be hurledat great force and cause personal injury to the operator or others inthe vicinity as well as damage the work and or equipment. Variousprocedures, devices and materials have been devised in an attempt tosafety reinforce the wheel and prevent fragments of a fractured wheelfrom being hurled therefrom. However, some of the devices are unpopularwith the operators and others obstruct or interfere with the grindingaction.

Heretofore cup shaped grinding wheels have been reinforced internally byimbedding, one or more preformed rings, straps or bands of various highstrength materials, in specific regions of the wheel in the mannerdisclosed in U.S. Pat. Nos. 2,250,580, 3,141,271 and 3,716,951. Othersare reinforced by molding combination mounting inserts or backing plateswith bent up flanges embedded only in the hub or mounting portion of thewheel as disclosed in U.S. Pat. Nos. 3,135,999, 3,278,301 and 3,204,371.Still others are safety reinforced externally by one or more separatebands or layers of high strength material bonded to or adjacent to theouter peripheral surfaces of the wheel as taught in U.S. Pat. Nos.2,800,754, 3,121,981 and 3,171,236.

However, unlike the applicant the prior art does not provide aninternally safety reinforced cup shaped wheel wherein the reinforcementor safety web extends continuously through the deeply recessed centralhub portion and into the annular sidewall portion whereby substantiallyall portions of the wheel are tied together. Hence the wheel of theinvention can be rotated safely at the higher speeds required in thisday and age. Should the wheel become fractured, the reinforcement willhold the fragments which are likely to cause injury, together andthereby prevent serious injury.

Applicant is also aware of the various resin bonded, reinforced,depressed or raised hub type portable wheels disclosed in U.S. Pat. Nos.2,540,112, 2,808,688, 2,997,820, 3,041,797 and 3,121,981. Molded withinsome of them are one or more parallel layers of continuous reinforcingmaterial which extends through the raised or depressed central hubportion, then bending slightly and continuing radially out through arelatively thin larger annular portion to the peripheral edge of thewheel. However, depressed cen ter wheels differ from the more deeplyrecessed shape wheels in that they are more flexible, relatively muchthinner, much easier to manufacture and reinforce due to the shallowrecess and the slight axialdisplacement of the central hub portion whichis of substantially the same thickness as the larger outer annularportion.

Heretofore, attempts have been made to manufac-,

ture and safety reinforce the relatively deeper cup type wheels by thesame method used to make the depressed center wheel. However due to thedeeper recess and mold cavity required to mold the cup wheel thereinforcement was bent sharply and fractured by the abrasive forced intocontact therewith. Hence, the reinforcement was ineffective since it didnot tie all portions of the wheel together, and the required quality,specifications and safety factor of the wheels varied widely and couldnot be consistently repeated.

Likewise multi-step molding methods of uniformly spreading abrasive mix,accurately placing and centering preformed safety reinforcing membertherein, and uniformly filling the deep cavity around it with additionalabrasive mix have not been entirely satisfactory, are more costly, andcomplicate the molding process. The applicants method and apparatus formolding the cup wheel of the invention differs from the prior artdisclosed in the above mentioned patents and in the additional followingU.S. Pat. Nos. Re. 20,460 and 3,705,248 in that the alternate layers ofabrasive bond mix and flexible safety reinforcement for each wheel areplaced and supported by a separate nonreusable thin flexible preformedsupport member supported within a mold band and above a mold cavity, bya narrow fixed outer ledge or surface and a movable support surface of amovable upwardly resiliently biased slideable central hub forming memberin a lower female die or mold plate. During molding the central portionof the layers are continuously compressed and held between the movingcentral hub forming portions of the upper mold plate and the movablecentral hub member while the surrounding outer portion of the layers,which form the sidewall portion of the wheel, are free to shift relativeto each other and thereby allow the reinforcement to bend smoothly aboutand from the fixed outer surface and assume a smoothly curved shape inthe mixture as they move into the cavity prior to being trapped andfinally compressed to final form. Each thin preformed support memberbeing molded to the wheel and its shape, may be left on, but, preferablyis removed from the molded wheel and disposed of.

SUMMARY OF THE INVENTION According to the invention cup shape grindingwheel has one or more layers of high strength safety reinforcingmaterial situated in, integrally molded and bonded within molded curableresinoid bonded abrasive mixture. Each layer of safety reinforcementextends or has elements which extend continuously, in a smoothly curvedshape, from an inner edge about the central hole radially outwardthrough the central hyb portion, then generally axially and radiallyoutward through the annular sidewall portion to an outer peripheral edgelocated initially at or adjacent a peripheral abrasive surface of thewheel. The safety reinforcement ties or connects the mounting or centralhub and annular sidewall portions of the wheel together so that brokenfragments thereof are held together and prevented for causing personalinjury. Also the curvature or curvilinear shape of the reinforcement issuch that, it is without sharp bends at which breaks are likely tooccur, the radial position of its outer peripheral edge variescontinuously as the axial length of the annular sidewall portion is reduced during grinding and does not materially interfere with grinding.

The invention also includes a method and apparatus for making theinternally safety reinforced resinoid bonded abrasive cup type grindingwheel. Essentially the method and apparatus comprises: supportingalternate layers of a suitable resin bond abrasive mix and flexiblereinforcing material on a thin flexible disk situated and supportedabove a lower portion of a mold cavity, by a fixed narrow outer annulartop surface of a lower female mold plate having a cavity adapted toshape the lowerouter peripheral surface of the cup shape wheel and aninner annular top surface of a central hub forming member slideablymounted, about a central hole, arbor, in the lower mold plate andresiliently biased upwardly within the cavity to the plane of the fixednarrow outer annular top surface. Thereafter, an upper male mold plateadapted to form the interior and the exterior radial grinding surface ofthe cup shape wheel is forced initially into engagement with only thecentral hub forming portion of the layers.

Then during further simultaneous movement of the upper mold plate andthe slideable central hub forming member, the inner central hub formingportions of the layers are continually held and partially compactedbetween them while the free outer annular sidewall forming portions ofthe layers of loose resin bond abrasive mix and reinforcement areallowed to and do shift slightly from their original relative positionsbecause the more rigid layers of flexible reinforcement have moreresistance to being bent sharply as it is forced into the cavity priorto being trapped and compressed to final size and shape.

Therefore it is the primary object of the invention to provide aninternally safety reinforced resinoid bonded abrasive cup shapedgrinding wheel wherein the safety reinforcement extends, continuously,in a smoothly curved shape, between and ties the central hub and annularsidewall portions of the wheel together, apparatus and method for makingthe wheel.

BRIEFv DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective verticalsectional view through the cup shaped wheel of the invention;

FIG. 2 is a vertical sectional view showing the relative positions ofthe parts of a mold assembly filled with and supporting alternate layersof abrasive resin bond mix and safety reinforcement above the moldcavity prior to being molded into a cup shape wheel; and

FIG. 3 is another vertical sectional view of the mold assembly showingthe relative positions of the abrasive layer and safety reinforcementand positions of the mold parts after the wheel has been molded.

DESCRIPTION OF THE PREFERRED EMBODIMENTS(S) Referring to FIG. 1 there isshown an internally safety reinforced cup shaped or type grinding wheelcomprised of a deeply recessed central hub or mounting portion 12. Onthe hub portion 12 are mounting means such as, the central hole 12a withor without a bushing therein shown extending between an inner orrecessed surface 12b and an outer or back surface 120 and through thehub portion about the central axis of the wheel. The mounting means mayfurther comprise a suitable insert or threaded bushing in the centerhole 12a adhesively or mechanically secured to the wheel as shown inphantom lines. The hub portion 12 has an exterior or outer tapered orfrusto conical shape surface 12a extending axially from the back surface120. Integrally molded with the central hub portion or mounting portion12 is an annular sidewall portion 14 of predetermined axial length ordepth and radial thickness extending around the central axis of thewheel. The annular sidewall portion has an internal or inner abrasivesurface 14a projecting, generally in an axial direction, from therecessed surface 12b to a junction with the inner edge of a radialgrinding face or surface 14b and an exterior peripheral grindingabrasive surface 14d tapering from the outer tapered surface 12d of thehub portion 12, to a junction with an outer or circumferential edge ofthe radial grinding surface 14b.

Preferably, the cup wheel 10 shown is what is known as a flared cup typewheel wherein the annular sidewall portion 14 tapers or flares outwardlyin both axial and radial directions from the central hub portion 12 andhas a central frusto conical shaped recess of predetermined depththerein.

Cup grinding wheels are also known as or designated by number whichindicates its general shape and dimension. The flared cup shapedgrinding wheel of the invention has what is generally known in the artas a type 1 1 shape, which the applicants have modified slightly toenhance the manufacture, and safety thereof without reducing itseffectiveness.

One or more layers or disks 16 of safety reinforcing material may beprovided for safety reinforcing the wheel against breakage at high speedincreasing the safety factor of wheel and holding fragments of a brokenor cracked wheel together to prevent personal injury. The safetyreinforcing layer or disk 16 may be preformed or cut out of any suitableand well known flexible sheet, foil or fabric of high strength materialssuch as metal, nylon, rayon, cotton, glass or combinations thereof.Preferably the reinforcement disks 16 are made of woven, braided orknitted open mesh fiber glass fabrics containing a plurality ofcontinuous strands or roving composed of a large number of continuousglass filaments. However, other types of high strength perforated sheetmaterial may be used.

One preferably suitable fiber glass material which was used to safetyreinforce the wheel 10 is designated as Lewcott Style No. 202, 2 X 2mesh or two openings per inch, of mock leno woven substantiallyuntwisted rovings of fiber glass fabric having a breaking strength of1,600 lbs. per inch and weighing 30 oz. per square yard before beingcoated with a thin layer of uncured thermosetting liquid resin andcommercially available from Lewcott Chemical and Plastics Corp.,Millbury, Mass.

Initially the layers 16 of safety reinforcing material are preformed orcut into flexible disks of predetermined diameter prior to being moldedor reformed to the smoothly bent curvature shown in FIGS. 1 and 3 duringmolding of the wheel 10.

As shown in FIG. 1 each reformed layer or safety disk 16 has a pluralityof spaced strands, tapes, rovings or elements 16a each consisting of aplurality of filaments which may extend continuously from either thecentral axis or an inner edge about the central hole 12a radiallyoutward through the central hub portion, then bending or curvingsmoothly therefrom into generally an axial direction through the annularsidewall portion and again bending or curving smoothly outwardly ingenerally a radial direction to an outer peripheral edge situated at oradjacent the exterior peripheral grinding surface 14d.

The composition of the molded and cured resin bonded abrasive mix usedto make the wheel may comprise any of the suitable and well 'knonwnatural or synthetic resins, abrasive particles, fillers, and grindingaids. For example, the abrasive particles may be of diamond, boronnitride, alumina, aluminazirconia, silicon carbide, garnet and mixturesthereof bonded to gether with the reinforcement 16 preferably by athermosetting resin such as, phenolic, or phenolformaldehyde resin, ureaformaldehyde resin, epoxy and combinations thereof in either the form ofa liquid coating on the grains or powder mixed with the abrasive.

The wheels may be cold or hot pressed to form and cured in theconventional manner at prescribed temperatures for a period of timesufficient to fully cure the resin bond and further comprise aninitially thin preformed flexible support member 50 molded to andforming a permanent backing on the surfaces 12d and 12c of the wheel asshown in FIG. 3.

A method of and apparatus for molding the cup wheel in accordance withthe invention will now be described in conjunction with FIGS. 2 and 3 ofthe drawings. Referring to FIG. 2. there is shown a molding apparatus ormold assembly 30 which is useable with and normally supported on the bedor lower platen P of either a hot or cold molding press of well knownsuitable and conventional design.

The mold assembly 30 comprises a mold band or hollow cylinder 32supported on the platen P of pressing means not shown and having acentral hole or cylindri cal aperture defined by and within the inner orinternal molding surface 320 of the desired peripheral shape of thewheel to be molded. Mounted within the lower por tion of the mold band32 and supported by the platen P is a lower female mold plate 34extending axially and vertically within the central hole between abottom surface 34a and an annular top surface 34b extending radiallybetween an inner side molding surface 34c in the lower portion of a moldcavity 34d and an outer surface 34e of the lower mold plate 34 adjacentsurface-32a of thgmold banci3 2 Alternatively the lower female moldplate 34 could be made an integral part of the mold band 32 and wherebythe annular top surface 3412 would extend to the internal surface 329defining the peripheral shape of the central hole or upper portion ofthe mold cavity M about the central axis of the mold assembly 36.

Slideably mounted with a central recess or counter bore 34f in the lowermold plate 34 is an adjustable central hub forming and/or support memberor movable support cylinder 36 with a central aperture or arbor hold 36aextending axially between an upper top annular hub forming surface 36band a lower or bottom surface 36c thereon. The central bore or recess34f extends from the bottom of the mold cavity 34d to a recessed bottomstop surface 34g, an axial depth substantially equal to the axial lengthof the hub support member 36. Hence when the surface 360 engages thestop surface 34g the upper hub support and forming top surface 36b willbe aligned to a horizontal plane with the bottom surface of the moldcavity 34d.

Biasing means, which may be of any suitable form and material, areprovided for biasing the central support member 36 upwardly into themold cavity 34d relative to the stop surface 343 and lower mold plate34. The biasing means shown comprises at least one but preferably aplurality of resilient compressible coil springs 38. Each of the springs38 has one end portion situated in and engaging the member 36 within ahole 36d and an opposite end portion engaging the lower mold plate 34within a recess 34h in the stop surface 34g. Alternatively a largersingle compression spring could be arranged around the central axis andrecessed into a single central hole or counter bore in the bottom of thehub support member 36 or the counter bore could serve as an air cylinderinto which compressible air is forced to raise the member 36.

Adjustable means are preferably provided for limiting the movement ofthe member 36, positioning and aligning the movable upper-annular or topsurface 36b of the hub forming member 36 on the same plane as the fixednarrow outer annular top surface 34b on the lower mold plate 34. Theadjustable means may be fixed but preferably comprise one or moreadjustable threaded screws or bolts 40 each with a threaded portionthreaded into a threaded hole in the lower portion of the member 36 andextending-therefrom through a clear counterbored hole 34h to a stopshoulder on the head portion of the screw 40 within the counterbore 341'of suitable depth. It can be seen that by adjusting the screw 40 theverticle position of the upper top surface 36b of the member can bealigned and maintained on the same plane with the outer annular surface34b of the lower mold plate 34. Also, "the depth of counterbore 341'must be deep enough to'allow sufficient free unobstructed movement ofthe head 40 and the member 36 to bottom against stop surface 34g.

l-Iole forming means are provided and supported by the lower mold plate34 for providing the cup shape wheels with any one of the desiredconventional mounting or drive means by which it can be mounted androtatably driven about its axis in the well known manner. The holeforming means shown comprises an elongated hole arbor 42 of the desiredcross sectional size and shape of the central hole 12a to be formed inthe wheel 16. The arbor 42 extends vertically and coaxially with theaxis of the mold assembly 30 from a lower end or bottom surface 34a ofthe: lower mold plate 34 through a support hole therein, the centralaperture 36a in the movable member 36 and the upper portion of the moldcavity to an upper or opposite end situated a sufficient distance abovethe top of the mold band 32 to receive an upper mold plate 44.

Obviously the mold assembly could be modified, for example, the arbor 42could be fixed to or made an integral part of the central hub supportmember 36 and movable therewith. Also, the bolts 40 could be eliminatedby making each spring 38 to the exact axial length sufficient to alignthe surfaces 36b and 34b on a single plane. When the wheel has no centerhole the arbor 42 is eliminated and replaced with suitable drive meanssuch as a threaded insert, bushing or another type of wheel mountingintegrally molded therewith or adhesively secured thereto in the wellknown manner. Alternatively the center hole could be bored after thewheel has been molded or fully cured.

The upper mold plate 44 which may be attached to and supported by theupper platen of a press has a central hole 44a into which the arbor 42extends and slideably engages the male mold plate 44 as it is forceablymoved in an axial direction relative to the arbor 42. The central hole44a extends coaxially with the axis of the arbor 42 between an upperpress platen engaging top surface 44b and a lower or central recess hubforming surface 440 substantially parallel to the surface 36b. Extendingupwardly and outwardly from the lower forming surface 440 is a frustoconical shape portion with a tapered exterior surface 44d extending toan intermediate or'annular radial surface 44e substantially parallel tothe surfaces 440 and 44b. The substantially flat surface 44a extendsradially outwardly to the circumferential or outer peripheral surface44f of a diameter or size and shape adapted to allow sliding engagementwith the surface 32a of the mold band 32.

Obviously the exterior surfaces 44c, 44d, 44e and 44f of the upper malemold plate will determine the final shape and size of the respectiveinterior surfaces 12b and 14a and the radial surface 14b of the cupwheel 10. Also, the interior surfaces 34c of the lower female mold plate34 and exterior top surface 36b of member 36 will shape the respectivesurfaces 120 and 12d of the cup wheel 10. Molding surface 32a of themold band 32 substantially parallel to the central axis and surface 34aof the lower mold plate 34 wil determine respectively the largercircumferential size or diameter and shape of the cup wheel and providean additional triangular shaped portion l4e, shown in phantom lines inFIG. 1 and which is preferably removed to form the tapered peripheralsurface 14d situated at an angle to the surface 12d.

The mold assembly 30 may further comprise flexible support means forsupporting and containing a load consisting of the layers of thecurablemixture of abrasive and bond and reinforcing material to be molded abovethe cavity between the movable and fixed support surfaces 36b and 34bduring the molding operation. Preferably the flexible means comprises areplaceable, nonreuseable and disposable thin flexible preformed member50 molded to the wheel and its shape and which may be left as a part ofthe wheel or removed therefrom as desired. Initially, each preformedsupport member extends horizontally across the mold cavity and issupported at its outer peripheral edge portion by the fixed narrow outersurface 34b, at its inner central portion by the movable surface 36b andhas an intermediate unsupported portion spanning the mold cavity below.

Preferably as shown in FIG. 2, a flexible support disks 50 of suitableflexibility, shape, strength and stiffness is preformed out ofsubstantially imperforate sheet material or closely woven fabricsufficient to contain the abrasive mix and has a center hole allowing itto be slipped over the hole arbor 42, and supported by the relativelyradially spaced top annular surfaces 36b and 34b. The support disk 50may be cut out of any suitable flexible sheet material, such as paper,plastic, cotton, rayon, nylon, fiber glass, metal, foil and combinationsthereof. However, either a single disk of crepe paper or a composite orlaminated support disk of paper stick glass cloth consisting of a layerof thin paper attached to a layer of open mesh fiber glass cloth foundto be satisfactory for supporting the alternate layers of abrasive resinmix 18 and reinforcement 16 without any appreciable sag into the cavity34d. A suitable glass cloth for the composite disk and final backingsecured to the wheel is designated a No. 955 consisting of woven lowtwist strands of glass fibers available from Eli Sandman Company,Worcester, Mass. When the disk 50 is a composite of paper and glasscloth it is placed in the mold with the thin paper side thereof incontact with the surfaces 34b and 36b and the open mesh glass cloth ontop whereby the abrasive mix 18 is prevented from passing into the lowerportion of the mold cavity 34d and the open mesh glass cloth becomesintegrally molded to the exterior surfaces of the wheel 10 after whichthe paper may if desired be peeled off and removed therefrom. To loadand prepare the mold assembly as shown in FIG. 2 for molding a cup wheela new replaceable support disk 50 is slipped over the arbor and placedon the supporting surfaces 36b and 34b for each wheel molded. A first orbottom layer of the desired loose abrasive resin mix 18 is spread andleveled to a predetermined depth upon the support dish 50 followed by atleast one or a first safety disk 16 and at least a second or top layerof the loose abrasive resin mix 18 if the wheel 10 is to have only onelayer or disk of internal safety reinforcement 16. Obviously when thecup wheel 10 is to have more than one layer of in-' ternal reinforcementthe depth of each layer of loose abrasive mix 18 spread on each layer ofsafety reinforcement 16 is reduced in proportion to the number of layersof safety reinforcement disks 16 desired. To provide the additionalstrength and a better safety factor the cup wheel 10 of the inventionmay have two but preferably three internal layers of safetyreinforcement 16. Hence, second and third disks of reinforcement 16 areplaced upon thinner second and third intermediate layers of abrasive mix18 and followed by a final top layer of the abrasive mix 18.

Alternatively, each layer 18 of the abrasive mix may be preshaped, andlightly prepressed into an uncured or green self supporting preformedlayer or disk of the abrasive bond mix. Each preformed layer or diskbeing lightly pressed and compressed to a thickness and degree whichwill allow handling and placing of the disks in the mold assembly andyet allow them to break up and crumble during the molding operation.

It can be seen that the horizontally extending layers of mix 18 andreinforcement disks 16 collectively provide a moldable load with anunpressed inner annular portion or central hub forming portion, aroundand adjacent to the hole arbor 42, resiliently supported by the innerannular movable surface 36b, an outer narrow annular portion thereofsupported by the fixed top annular surface 34b of the lower mold plate34 and between them an intermediate annular portion or annular sidewallforming portion supported by the flexible support disk 50 spanning thelower portion of the mold cavity 34d.

After, the upper portion of mold cavity in the mold band 32 has thedesired number of layers of mix and reinforcement, the upper mold plate44 is slipped over the exposed upper end portion of the hole arbor 42 sothat the inner or lower surface 44c engages only the inner annularportion of the top layer of abrasive mix 18.

The loaded mold assembly 30 if not on the lower platen P of aconventional molding press is transferred thereto and aligned with theupper platen of the press or the upper mold plate if attached thereto.Then the press is actuated which forces the upper and lower mold platesto move relative to and toward each other and partially compact thecentral annular portion of the mix 18 between surface 36b of theresiliently biased movable member 36 and surface 440 of upper mold plateprior to overcoming the total resistance of the springs 38 and movementof the member 36 thereby.

Depending on the total spring resistance, which is predetermined and canbe varied by substituting springs made of lighter or heavier wire, thecentral annular portion of the mix 18 may be reduced to an axial depthor dimension up to one-third less than the initial total load thicknessbefore the total resistance of the springs is overcome.

In FIG. 2 there is shown in phantom line the partially displacedposition of the upper mold plate 44 and the partially compressed centralportion of mix 18 and safety disks 16. It can be seen that thesurrounding intermediate and outer annular portions of the layers of mix18 and reinforcement 16 are free to shif relative to each other and thelower mold plate 34 until the surfaces 44e of the upper mold plate hasmoved down to entrap the mix and compress the outer annular portion ofthe mix between the fixed surfaces 34b and movable surface 44csufficiently to prevent further relative movement in the outer annularportion only.

Further, downward movement of the upper mold plate 44 causessimultaneous movement of the partially compressed central portion of themix 18 into the lower portion of the mold cavity 34d, and the movablemember 36, in the counter bore 34f, which continuously compresses,increases the resistance and the force exerted by the springs 38 againstthe member 36 further compressing the central portion of the mix l8prior to engaging the stop surface 343.

As the partially compressed central portion of the mix 18 and member 36move together into the lower mold cavity relative to the fixed outerannular surface 34b the intermediate annular portion of the mix istrapped and forced by the tapered or conical surface 44d of the uppermold plate 44 to flow into the lower portion of the mold cavity 34d. Thesurrounding intermediate annular portion of the mix 18 remainssubstantially unpressed until it moves into engagement with the taperedsurface 34c of the lower mold cavity 34d of frusto conical shape. Sincethe outer annular portion of mix 18 above the fixed top surface 34b ispartially compressed before and to a greater degree than the adjacentintermediate portion, the narrow outer annular portion adjacent theouter peripheral edges of each disk 16 and of the support disk 50 isfirmly gripped by the partially compressed mix therein. The inner orcentral annular portion adjacent the inner edge of each of the disks 16around the central hole is also firmly gripped and substantially fixedagainst radial movement of the arbor 42 and the compressed and movablecentral annular portion of the mix 18 aroung the arbor is compressed toa greater degree than and prior to the outer annular portion of the mix18.

During the downward movement the flexible disks 16, which have a greaterresistance to bending than the relatively unpressed loose granularintermediate annular portion of the mix 18, move through and repositionthemselves in the mix and bend gradually into a smoothly curved shape bydisplacing and allowing the abrasive mix 18 to pass through the openingstherein prior to being reformed to the final shape of curvature.

Each of the flexible disks 16 are drawn inwardly and move radiallyrelative to the intermediate and outer annular portion of the mix asthey assume a smooth bending curvilinear shape or internal path'ofcurvature extending between their inner edge in the central portion totheir outer peripheral edge in the outer annular portion of the mix.Obviously the length of the smoothly bending curvature of each reformedsafety disk 16 is substantially equal to the initial radius or radialdistance between the hole and the outer peripheral edge of the disk 16prior to being reformed and molded in the wheel 10.

When the movable member 36 reaches and engages the stop surface 34g itsupper top surface 36b will be aligned substantially with the surroundingfixed bottom surface of the lower mold cavity and which together providea solid bottom surface against which the mix is pressed to final sizeand shape. As shown in FIG. 3 the mix 13 is further compressed andmolded to the desired size and shape determined by the mold assembly ata pressure of between 1 and 4 tons per square inch applied thereto bythe press.

If desired the mold assembly 30 may be constructed so that it can beheated in any suitable well known conventional manner or used in contactwith and heated by the heatable platens of a conventional hot press toeither partially or completely cure the resin and bond the mix 18 andthe safety disks 16 together. The wheels after being pressed to shapeare stripped from the mold in the conventional way such as by separatingthe mold plates whereupon the released compressed springs resilientlyforces the member 36 and molded wheel upwardly out of the lowercavityfrom which it may be removed. Another method would be by axiallydisplacing the upper and lower mold plates 34 and 44 relative to and outof the mold band 32, the arbor 42 out of the upper mold plate 44 and themolded wheel 10, remo ving the upper mold plate 44 from the inner orcentral cavity of the wheel and the wheel from the cavity in the lowermold plate 34.

Next, the molded and reformed thin support diskSll, which may be lefton, is preferably peeled off or re moved in any suitable manner fromthe-exterior surfaces of the wheel.

The cold pressed green wheel is then placed in between a pair ofpressure setting plates, batts, or supports preformed to the shape ofthe upper and lower mold plates 34 and 44 and which :apply about 2pounds per square inch of pressure to maintain the molded shape andbaked in an oven for 15 hours at a temperature of C until the resin hascompletely cured and bonded the abrasive mix and the safety disks 16into a rigid integral structure. After curing, the assembly of settingplates and the wheel are removed from the oven allowed to cool and thewheel separated therefrom.

The cured wheel which has substantially the same cross sectional shapeas that shown in FIG. 3 can be left and used with that configurationwhich includes an upper sidewall portion with an outer cylindricalperipheral or circumferential surface 14f, sugstantially parallel to thecentral axis, formed by and to the same diam eter or size as theengaging surface 320. The surface 14f extends between the annular radialsurface 14b formed by the engaging surface 44a and an intermediatenarrow outer annular radial surface ll4g formed by the engaging fixedsurface 34b. When compared with the preferred cross sectional shape ofthe wheel 10 ure. The results were as follows:

shown in FIG. 1, it can be seen that the cured wheel must be furtherprocessed to remove a triangular shaped portion l4e within the initialmolded surfaces 14f and 14g as indicated by phantom lines and thedesired outer tapered periphery abrasive surface 14d shown in FIG. 1.The triangular portion 14c is preferably removed by a truing orreshaping operation which reshapes the wheel to have the upper frustoconical shaped or tapered outer peripheral surface 14d around the flaredannular sidewall portion 14 extending from the lower or adjacent thefrusto conical shape or tapered outer peripheral surface 140 around thecentral hub portion 12. The surfaces 12d and 14d shown are situated atan angle to each other and inclined at different angles fromthe centralvertical axis and the horizontal plane at bottom surface 120 normal tothe gep t r2 1 l axis of the wheel.

A group of internally reinforced resinoid bonded abrasive flaring cupwheels of the invention were made, each purposely cracked at four places90 apart and speed tested to failure. The cracked wheels tested had anannular sidewall peripheral surface 14d tapering from a mazimum outsidediameter of 6 inches to inches diameter, a 1% inch diameter center hole120 with a threaded bushing adhesively secured therein, a 1%. inch thickcentral hub portion 12 with the surface 12b recessed 1% inches from theradial surface 14b and a surface 12d tapering from the 5 inch diameterto the back surface 120 of approximately 3 inches in diameter all moldedfrom the same premixed batch of mix but a with a different number ofidentical safety discs 16 therein of style No. 202 described above.

The premixed batch of abrasive mix from which the wheels were molded wascomprised of the following percentage by weight of the ingredientslisted below:

Ingredients by Wt.

16 grit aluminum oxide abrasive grain 77.53 Bakelite No. 5980 powderedthermosetting resin 9.26 325 mesh glass spheres (filler) 8.40 lime (CaO)1.84 carbon black .20 (Carbosota) refined Creosote .99 furfural(plasticizer) 1.78

disks or webs are capable of being operated safely at' 14,000 surfacefeet per minute (s.f.p.m.) without any fear of failure and personalinjury.

A series of 6 inch cup wheels of the invention each with three safetydisks were also made in five different grades or degrees of hardness andspeed tested to fail- Average Speed (s.f.p.m.)

Grade No. of Wheels At F allure Softer l 3 22,600 2 3 23,900 3 3 24,5004 3 25,700

Harder 5 3 26,200

From the above data wheels of increasing hardness and grade indicated bythe larger number failed at proportionately higher surface feet perminute (s.f.p.m.) than the softer grades and are likewise capable ofbeing safely operated at proportionately higher operating speeds greaterthan 14,000 surface feet per minute.

It is to be understood that the disclosure hereinabove is for thepurpose of illustration only and the the invention includes allmodifications and equivalents which fall within the scope of theappended claims.

We aim; 1. An internally safety reinforced cup type resinoid bondedabrasive grinding wheel comprisingz i a recessed central hub portion ofpredetermined axial thickness extending radially between a relativelydeep recess in one side of the grinding wheel and an opposite side ofthe grinding wheel to an exterior peripheral surface of the hub portionand wheel and including substantially the entire opposite side of thegrinding wheel; means in the central hub portion for mounting androtating the wheel about a central axis; an annular sidewall portion ofpredetermined radial thickness and initial axial length reduceableduring grinding, integrally molded with the hub portion, extendingaround the central axis and the recess and generally axially from therecessed central hub portion to the one side of the wheel and having aradial grinding surface on the one side of the grinding wheel and anexternal peripheral surface adjacent to and extending from the radialgrinding surface to a junction with the exterior peripheral surface ofthe hub portion and wheel; and at least one internal layer of safetyreinforcing material integrally molded within and bonded to the centralhub and sidewall portions and having a smoothly curved shape extendingcontinuously generally radially outward through the central hub portion,then generally both axially and radially outward in a continuouslycurving path through the annular sidewall portion to an outer peripheraledge;

whereby the continuous internal safety reinforcing material is bonded toand continuously interconnects the central hub and sidewall portions ofthe wheel, has no sharp bends at which breaks are likely to occur,permits the wheel to be operated safely at high speed, holds fragmentsof the wheel which may be accidentally broken together and therebyprevent them from being hurled at high speed and causing personal injuryand the radial position of the outer peripheral edge once exposed at theradial grinding surface varies as the axial length of sidewall portionis reduced during grindmg.

3. An internally safety reinforced cup type resinoid bonded abrasivegrinding wheel according to claim 2, further comprising:

a third internal layer of safety reinforcing material spaced from thesecond internal layer of safety reinforcing material, integrally moldedwithin and bonded to the central hub and sidewall portions and having asmoothly curved shape extending continuously generally radially outwardthrough the central hub portion, then generally axially and radiallyoutward through the sidewall portion to an outer peripheral edge.

4. An internally safety reinforced cup type resinoid bonded abrasivegrinding wheel according to claim 3 wherein each of the internal layersof safety reinforcing material comprises a layer of open mesh wovenfiber glass fabric.

5. An internally safety reinforced cup type resinoid bonded abrasivegrinding wheel according to claim 4 wherein the open mesh fiber glassfabric comprises:

a plurality of woven roving each having a plurality of continuoussubstantially untwisted glass filaments.

6. An internally safety reinforced cup type resinoid bonded abrasivegrinding wheel according to claim 5 further comprising:

a frusto conical shaped recess situated within the annular sidewallportion and adjacent the central hub portion, and

wherein the recessed central hub portion further comprises:

LII

an inner surface located initially a predetermined axial depth from theradial grinding surface, and spaced from the opposite side of the wheeland a tapered exterior peripheral surface flaring radially outward froman outer peripheraledge of the opposite side of the wheel to a junctionwith the external peripheral surface of the annular sidewall portion.

7. An internally safety reinforced cup type resinoid bonded abrasivegrinding wheel according to claim 6 wherein the annular sidewall portionfurther comprises:

a tapered external peripheral surface extending from a junction with thetapered exterior surface of the central hub portion and flaring radiallyoutwardly relative to the central axis to a junction with an outer edgeof the radial grinding surface.

8. An internally safety reinforced cup type resinoid bonded abrasivegrinding wheel according to claim 6 wherein the annular sidewall portionhas a straight external peripheral surface of predetermined axial lengthextending substantially parallel to the central axis from a junctionwith an outer edge of the radial grinding surface, and

a narrow intermediate radial surface spaced from the radial grindingsurface and extending radially outward from the tapered exteriorperipheral surface of the central hub portion to a junction with thestraight external peripheral surface.

1. An internally safety reinforced cup type resinoid bonded abrasivegrinding wheel comprising: a recessed central hub portion ofpredetermined axial thickness extending radially between a relativelydeep recess in one side of the grinding wheel and an opposite side ofthe grinding wheel to an exterior peripheral surface of the hub portionand wheel and including substantially the entire opposite side of thegrinding wheel; means in the central hub portion for mounting androtating the wheel about a central axis; an annular sidewall portion ofpredetermined radial thickness and initial axial length reduceableduring grinding, integrally molded with the hub portion, extendingaround the central axis and the recess and generally axially from therecessed central hub portion to the one side of the wheel and having aradial grinding surface on the one side of the grinding wheel and anexternal peripheral surface adjacent to and extending from the radialgrinding surface to a junction with the exterior peripheral surface ofthe hub portion and wheel; and at least one internal layer of safetyreinforcing material integrally molded within and bonded to the centralhub and sidewall portions and having a smoothly curved shape extendingcontinuously generally radially outward through the central hub portion,then generally both axially and radially outward in a continuouslycurving path through the annular sidewall portion to an outer peripheraledge; whereby the continuous internal safety reinforcing material isbonded to and continuously interconnects the central hub and sidewallportions of the wheel, has no sharp bends at which breake are likely tooccur, permits the wheel to be operated safely at high speed, holdsfragments of the wheel which may be accidentally broken together andthereby prevent them from being hurled at high speed and causingpersonal injury and the radial position of the outer peripheral edgeonce exposed at the radial grinding surface varies as the axial lengthof sidewall portion is reduced during grinding.
 2. An internally safetyreinforced cup type resinoid bonded abrasive grinding wheel according toclaim 1 further comprising: a second internal layer of safetyreinforcing material spaced from the at least one internal layer ofsafety reinforcing material, integrally molded within and bonded to thecentral hub and sidwall portions and having a smoothly curved shapeextending continuously generally radially outward through the centralhub portion then generally axially and radially outward through thesidewall portion to an outer peripheral edge.
 3. An internally safetyreinforced cup type resinoid bonded abrasive grinding wheel according toclaim 2, furthEr comprising: a third internal layer of safetyreinforcing material spaced from the second internal layer of safetyreinforcing material, integrally molded within and bonded to the centralhub and sidewall portions and having a smoothly curved shape extendingcontinuously generally radially outward through the central hub portion,then generally axially and radially outward through the sidewall portionto an outer peripheral edge.
 4. An internally safety reinforced cup typeresinoid bonded abrasive grinding wheel according to claim 3 whereineach of the internal layers of safety reinforcing material comprises alayer of open mesh woven fiber glass fabric.
 5. An internally safetyreinforced cup type resinoid bonded abrasive grinding wheel according toclaim 4 wherein the open mesh fiber glass fabric comprises: a pluralityof woven roving each having a plurality of continuous substantiallyuntwisted glass filaments.
 6. An internally safety reinforced cup typeresinoid bonded abrasive grinding wheel according to claim 5 furthercomprising: a frusto conical shaped recess situated within the annularsidewall portion and adjacent the central hub portion, and wherein therecessed central hub portion further comprises: an inner surface locatedinitially a predetermined axial depth from the radial grinding surface,and spaced from the opposite side of the wheel and a tapered exteriorperipheral surface flaring radially outward from an outer peripheraledge of the opposite side of the wheel to a junction with the externalperipheral surface of the annular sidewall portion.
 7. An internallysafety reinforced cup type resinoid bonded abrasive grinding wheelaccording to claim 6 wherein the annular sidewall portion furthercomprises: a tapered external peripheral surface extending from ajunction with the tapered exterior surface of the central hub portionand flaring radially outwardly relative to the central axis to ajunction with an outer edge of the radial grinding surface.
 8. Aninternally safety reinforced cup type resinoid bonded abrasive grindingwheel according to claim 6 wherein the annular sidewall portion has astraight external peripheral surface of predetermined axial lengthextending substantially parallel to the central axis from a junctionwith an outer edge of the radial grinding surface, and a narrowintermediate radial surface spaced from the radial grinding surface andextending radially outward from the tapered exterior peripheral surfaceof the central hub portion to a junction with the straight externalperipheral surface.